A good maintenance mode plugin that with Memberships and leaves gateways working?

I need to put my site in maintenance mode, but still allow the Paypal to hit my return to confirm Membership signups.

I'm thinking this one would be good since I can make exceptions by IP, assuming I can figure out all the paypal sandbox IP addresses.

http://wordpress.org/extend/plugins/jf3-maintenance-mode/screenshots/

I just thought I would check to see if anyone had a better idea.